Port most of the functions found in ec/acpi/ec.c to ACPI Source Language
(ASL). These functions are used to control embedded controllers with the
standard ACPI interface (mostly through i/o ports 0x62 / 0x66).

The following methods are implemented and tested against the power
managements channels of a ITE IT8516E embedded controller:
* WAIT_EC_SC Wait for a bit in the EC_SC register
* SEND_EC_COMMAND Send one command byte to the EC_SC register
* SEND_EC_DATA Send one data byte to the EC_DATA register
* RECV_EC_DATA Read one byte of data from the EC_DATA register
* EC_READ Read one byte from ec memory (through cmd 0x80)
* EC_WRITE Write one byte to ec memory (through cmd 0x81)

To use the provided methods, one should include `ec/acpi/ec.asl` in the
EC device code. Prior doing so, two macros should be defined to identify
the used i/o ports:
* EC_SC_IO I/o address of the EC_SC register
* EC_DATA_IO I/o address of the EC_DATA register